[SOLVED] Expectation of a Conditional Distribution

I am stuck in this problem

Let X and Y have the joint pdf $\displaystyle f(x,y)=1, -x<y<x, 0<x<1, $ zero elsewhere. Show that, on the set of positive probability density, the graph $\displaystyle E(Y|x)$ is a straight line whereas that of $\displaystyle E(X|y)$ is not a straight line.